Tom Hanks races through a graceful Roman piazza, past an ancient Egyptian obelisk surrounded by fountains of water-spouting lions, his eyes focused on a church tucked into the corner of the square. Moviegoers know that his character, Robert Langdon, is trying desperately to stop a grisly murder, following a trail of secret clues laid down nearly four centuries ago by the scientist Galileo and the baroque sculptor and architect Gianlorenzo Bernini. What they don’t know is that this graceful piazza itself harbors a dark secret.

Piazza del Popolo—and its namesake church, where Langdon is headed—was built to evict Nero’s ghost. This had been the hated emperor’s ancient family estate, and his likely burial spot, and area residents had for centuries complained that Nero’s evil spirit haunted a pine grove on the site. Finally, the Vatican chopped down the trees, exorcized the site, and built the piazza and its church “of the people.”

Many of Rome’s important sites are featured in Angels & Demons, the latest codes-and-clues thriller courtesy of author Dan Brown, director Ron Howard, and leading man Tom Hanks. These Roman spots are full of secrets and scandals, and while the movie reveals several—and invents a few more to serve its plot involving Illuminati assassins and Renaissance intellectuals—the true miraculous and demonic events that took place at them are often even stranger than those Dan Brown’s imagination could whip up.

First, a reality check: the movie’s church interiors aren’t the real deal. Howard wasn’t allowed to film inside any of them, especially in the Vatican. (Actually, no one can shoot movies in the Vatican, not even the producers of the official John Paul II biopic.) However, plenty of the exteriors are genuine, and Roman life occasionally intruded on filming. At one point, Hanks reportedly halted production to help a bride cut through the set—even holding her train—so she wouldn’t be late for her wedding inside the Pantheon.

What the movie doesn’t say, though, is that the Pantheon—an ancient pagan shrine that survived barbarian sackings and became a church in AD 609—was pillaged by none other than a pope. In the 1600s, Pope Urban VIII (a member of the powerful Barberini family) seized the bronze revetments from the Pantheon portico’s ceiling and had them melted down to make cannons for the papal stronghold, Castel Sant’Angelo. (The act led to the infamous phrase, “That which even the barbarians wouldn’t do, Barberini did.”)

We’ve rounded up the inside scoop on the movie’s most noteworthy sites and crafted a tour that follows in the footsteps of Robert Langdon but goes well beyond Angels & Demons to reveal some of the even weirder—and true—sagas, scandals, and miracles of the Eternal City. When you go see the movie, keep our handy guide close (spoiler alerts ahead, however!) while you’re reaching for the popcorn.